1. Field of the Invention
The present invention relates to a catalyst component for use in the polymerization of .alpha.-olefins. More specifically, the present invention relates to a catalyst component, which makes possible the production of .alpha.-olefin polymers having a high melting point, a catalyst for the polymerization of .alpha.-olefins using said catalyst component, and a process for producing .alpha.-olefin polymers using said catalyst.
2. Related Art
A so-called Kaminsky catalyst has been well known as a homogeneous catalyst for the polymerization of olefins. This catalyst is characterized in that it has a very high catalytic activity for the polymerization and can provide a polymer with a narrow molecular weight distribution.
As transition metal compounds useful for the production of isotactic polyolefins by Kaminsky catalyst, ethylenebis(indenyl)zirconium dichloride and ethylenebis(4,5,6,7-tetrahydroindenyl)zirconium dichloride (Japanese Patent Laid-Open Publication No. 130314/1986) have been known. They, however, have disadvantages including that the resultant polyolefins have a low molecular weight and polymerization at a low temperature can provide high-molecular weight polyolefins only at the sacrifice of the polymerization activity of the catalyst. Further, it has been known that a high-molecular weight polymer can be produced when a hafnium compound is used instead of zirconium as a transition metal compound (Journal of Molecular Catalysis, 56 (1989) p. 237-247). However, this method may, to the best of our knowledge, have a shortcoming in that the polymerization activity is low.
Furthermore, dimethylsilylbis-substituted cyclopentadienylzirconium dichloride and the like are proposed in Japanese Patent Laid-Open Publication No. 301704/1989, Polymer Preprints, Japan Vol. 39, No. 6, p. 1614-1616 (1990) and Japanese Patent Laid-Open Publication No. 12406/1991, and dimethylsilylenebis(indenyl)zirconium dichloride and the like are proposed in Japanese Patent Laid-Open Publication Nos. 295007/1988 and 275609/1989. These proposals may have made possible the production of polymers having a high stereoregularity and a high melting point by polymerization at relatively low temperatures. To the best of our knowledge, however, a lowering in the stereoregularity, melting point and molecular weight of the polymers would be significant when the polymerization is carried out under high temperature conditions that are favorable from the viewpoint of economy.
Japanese Patent Laid-Open Publication Nos. 268307/1992 and 268308/1992 suggest that the stereoregularity and molecular weight can be improved to some extent when use is made of cyclopentadienyl compounds as referred to above which have a substituent to the position (2-position) adjacent to the crosslinking group in the cyclopentadienyl compounds. This method, however, would still be unsatisfactory in the performance under polymerization conditions of an increased polymerization temperature regarded as advantageous from the viewpoint of economy.
An object of the present invention is to provide a catalyst component for the polymerization of .alpha.-olefins, by which catalyst extrudable and injection-moldable olefin polymers having a high molecular weight and a high melting point can be obtained in a high yield, a catalyst for the polymerization of .alpha.-olefins and a process for producing .alpha.-olefin polymers.